The History of the General Education Basic FormulaBasic Formula Chart - IPD and CPIBasic Formula Chart - IPDBasic Formula Chart - CPINOTE: Consumer Price Index (CPI) calculates inflation based on a basket of goods that a consumer would purchase. Substitutions are allowed, such as swapping pears for apples based on availability and price. The Implicit Price Deflator (IPD) is based on the cost of state and local government expenditures, which can be a more accurate measure of inflation than CPI for labor intensive entities like education that face significant price pressures like decades-long double-digit increases for employee health insurance.